Surface mapping using an intraoral scanner with penetrating capabilities

ABSTRACT

An exemplary optical apparatus has an OCT imaging apparatus with a first light source for low coherence light of wavelengths above a threshold wavelength and a signal detector that obtains an interference signal between low coherence light from the sample and low coherence light reflected from a reference. A surface contour imaging apparatus has a second light source that emits one or more wavelengths of surface illumination below the threshold wavelength, a camera to acquire images from illumination reflected from the sample. The exemplary optical apparatus and/or exemplary methods for using the same can provide reduced errors in generating a dental 3D surface mesh.

FIELD OF THE INVENTION

The disclosure relates generally to apparatus for optical coherencetomography imaging and more particularly to apparatus that combine depthimaging from optical coherence tomography with surface contour imagingcapability.

BACKGROUND OF THE INVENTION

Optical coherence tomography (OCT) is a non-invasive imaging techniquethat employs interferometric principles to obtain high resolution,cross-sectional tomographic images that characterize the depth structureof a sample. Particularly suitable for in vivo imaging of human tissue,OCT has shown its usefulness in a range of biomedical research andmedical imaging applications, such as in ophthalmology, dermatology,oncology, and other fields, as well as in ear-nose-throat (ENT) anddental imaging.

OCT has been described as a type of “optical ultrasound”, imagingreflected energy from within living tissue to obtain cross-sectionaldata. In an OCT imaging system, light from a wide-bandwidth source, suchas a super luminescent diode (SLD) or other light source, is directedalong two different optical paths: a reference arm of known length and asample arm that illuminates the tissue or other subject under study.Reflected and back-scattered light from the reference and sample arms isthen recombined in the OCT apparatus and interference effects are usedto determine characteristics of the surface and near-surface underlyingstructure of the sample. Interference data can be acquired by rapidlyscanning the sample illumination across the sample. At each of severalthousand points, OCT apparatus obtains an interference profile which canbe used to reconstruct an A-scan with an axial depth into the materialthat is a factor of light source coherence. For most tissue imagingapplications, OCT uses broadband illumination sources and can provideimage content at depths of a few millimeters (mm).

Initial OCT apparatus employed a time-domain (TD-OCT) architecture inwhich depth scanning is achieved by rapidly changing the length of thereference arm using some type of mechanical mechanism, such as apiezoelectric actuator, for example. TD-OCT methods use point-by-pointscanning, requiring that the illumination probe be moved or scanned fromone position to the next during the imaging session. More recent OCTapparatus use a Fourier-domain architecture (FD-OCT) that discriminatesreflections from different depths according to the optical frequenciesof the signals they generate. FD-OCT methods simplify or eliminate axialscan requirements by collecting information from multiple depthssimultaneously and offer improved acquisition rate and signal-to-noiseratio (SNR). There are two implementations of Fourier-domain OCT:spectral domain OCT (SD-OCT) and swept-source OCT (SS-OCT).

SD-OCT imaging can be accomplished by illuminating the sample with abroadband source and dispersing the reflected and scattered light with aspectrometer onto an array detector, such as a CCD (charge-coupleddevice) detector, for example. SS-OCT imaging illuminates the samplewith a rapid wavelength-tuned laser and collects light reflected duringa wavelength sweep using only a single photodetector or balancedphotodetector. With both SD-OCT and SS-OCT, a profile of scattered lightreflected from different depths is obtained by operating on the recordedinterference signals using Fourier transforms, such as Fast-Fouriertransforms (FFT), well known to those skilled in the signal analysisarts.

For surface imaging of the teeth, various methods using lighttriangulation have been employed. These include structured lightimaging, in which a structured pattern of light, generally of visible ornear-visible infrared (NIR) wavelengths, is directed onto the toothsurface and the resulting pattern, modulated by the tooth surface, isdetected by a camera. Interpretation of distortion of the projectedpattern in the acquired images enables an accurate characterization ofthe tooth surface. The detected image information can be used, forexample to form a mesh or point cloud that maps features of the toothsurface and can be used, along with other types of depth imaging, toprovide useful information that can aid in dental diagnosis andtreatment.

The combined results from OCT and structured light imaging can provideuseful information for dental imaging. Proposed approaches for obtainingthis combination in a single apparatus solution, however, have beencharacterized by a number of problems, including optical crosstalkbetween measurement types, difficulties in achieving optimal imagequality in simultaneous surface and OCT measurements, workflowconstraints, and computational complexity, with considerable processingoverhead. Clearly, there would be advantages for improved performanceand workflow using a dental imaging device that combines OCT and surfacecontour imaging capabilities.

SUMMARY OF THE INVENTION

An aspect of this application is to advance the art of dental imagingsystems.

Another aspect of this application is to address in whole or in part, atleast the foregoing and other deficiencies in the related art.

It is another aspect of this application to provide in whole or in part,at least the advantages described herein.

It is an object of the present disclosure to advance the art ofdiagnostic imaging and to address the need for simultaneous ornear-simultaneous OCT and surface contour imaging and for registeringOCT depth data to surface contour information. An embodiment of thepresent invention provides apparatus and methods that enable both typesof imaging to be performed from a single device, configured to acquireeither or both surface contour and OCT depth imaging content.

According to an aspect of the application, there is provided a methodfor imaging a sample comprising:

a) obtaining optical coherence tomography imaging content with steps of:

-   -   (i) generating low coherence light of wavelengths above a        threshold wavelength;    -   (ii) obtaining an interference signal between a first portion of        the low coherence light scattered from the sample and a second        portion of the low coherence light reflected from a reference;

b) obtaining surface contour imaging content;

c) simultaneously to step b) obtaining depth imaging content associatedto the obtained surface contour imaging content;

d) segmenting among the depth imaging content a non deformable imagingcontent; and

where optical coherence tomography imaging and surface contour imagingcontent are obtained and mapped to the same coordinate system using thenon deformable content.

In a further aspect of the application, the method further comprisesproviding a CBCT scan 3D image of the sample; and registering the nondeformable content with CBCT Scan 3D image.

These objects are given only by way of illustrative example, and suchobjects may be exemplary of one or more embodiments of the invention.Other desirable objectives and advantages inherently achieved by thedisclosed methods may occur or become apparent to those skilled in theart. The invention is defined by the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features, and advantages of theinvention will be apparent from the following more particulardescription of the embodiments of the invention, as illustrated in theaccompanying drawings.

The elements of the drawings are not necessarily to scale relative toeach other. Some exaggeration may be necessary in order to emphasizebasic structural relationships or principles of operation. Someconventional components that would be needed for implementation of thedescribed embodiments, such as support components used for providingpower, for packaging, and for mounting and protecting system optics, forexample, are not shown in the drawings in order to simplify description.

FIG. 1 is a schematic diagram that shows a programmable filter accordingto an embodiment of the present disclosure.

FIG. 2A is a simplified schematic diagram that shows how theprogrammable filter provides light of a selected wavelength band.

FIG. 2B is an enlarged view of a portion of the micro-mirror array ofthe programmable filter.

FIG. 3 is a plan view that shows the arrangement of micro-mirrors in thearray.

FIG. 4 is a schematic diagram that shows a programmable filter using aprism as its dispersion optic, according to an alternate embodiment ofthe present disclosure.

FIG. 5 is a schematic diagram showing a programmable filter thatperforms wavelength-to-wavenumber transformation, according to analternate embodiment of the present disclosure.

FIG. 6A is a schematic diagram showing a swept-source OCT (SS-OCT)apparatus using a programmable filter according to an embodiment of thepresent disclosure that uses a Mach-Zehnder interferometer.

FIG. 6B is a schematic diagram showing a swept-source OCT (SS-OCT)apparatus using a programmable filter according to an embodiment of thepresent disclosure that uses a Michelson interferometer.

FIG. 7 is a schematic diagram that shows a tunable laser using aprogrammable filter according to an embodiment of the presentdisclosure.

FIG. 8 is a schematic diagram that shows use of a programmable filterfor selecting a wavelength band from a broadband light source.

FIG. 9 shows galvo mirrors used to provide a 2-D scan as part of the OCTimaging system probe.

FIG. 10A shows a schematic representation of scanning operation forobtaining a B-scan.

FIG. 10B shows an OCT scanning pattern for C-scan acquisition.

FIG. 11 is a schematic diagram that shows components of an intraoral OCTimaging system.

FIG. 12 is a process flow diagram that shows a sequence for OCTprocessing according to an embodiment of the present disclosure.

FIGS. 13A-13E show different types of imaging content acquired andgenerated as part of the OCT processing sequence, using the example of atooth image having a severe cavity.

FIG. 14 is a perspective view that shows a pattern of light projectedonto a contoured surface.

FIG. 15 is a schematic diagram showing components of an imagingapparatus for combined OCT and surface contour imaging.

FIG. 16A is a schematic diagram showing an imaging apparatus having ahandheld probe for combined OCT and surface contour imaging.

FIG. 16B is a schematic diagram showing an imaging apparatus thatcombines surface contour and OCT imaging.

FIG. 17A is a schematic view that shows a probe configuration using asingle two-axis scanning mirror.

FIG. 17B is a schematic view that shows an alternative probeconfiguration using a single two-axis scanning mirror and a lens that isshared by both projection and imaging light paths.

FIG. 17C is a schematic view that shows a probe configuration using atwo-mirror, two-axis scanner.

FIG. 17D is a schematic view that shows a probe configuration using asingle two-axis scanning mirror without separate focusing optics.

FIG. 17E is a schematic view that shows a probe configuration combiningOCT scanning with external line sweeping.

FIG. 17F is a schematic view that shows the second configurationcombining OCT scanning with external line sweeping.

FIG. 18 shows a light source selection guide for the different types ofimaging provided from the apparatus of the present disclosure.

FIG. 19 depicts an overall schematic perspective view of an extra-oralCBCT imaging apparatus according to an embodiment of the invention;

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following is a detailed description of exemplary embodiments,reference being made to the drawings in which the same referencenumerals identify the same elements of structure in each of the severalfigures.

Where they are used in the context of the present disclosure, the terms“first”, “second”, and so on, do not necessarily denote any ordinal,sequential, or priority relation, but are simply used to more clearlydistinguish one step, element, or set of elements from another, unlessspecified otherwise.

As used herein, the term “energizable” relates to a device or set ofcomponents that perform an indicated function upon receiving power and,optionally, upon receiving an enabling signal.

In the context of the present disclosure, the term “optics” is usedgenerally to refer to lenses and other refractive, diffractive, andreflective components or apertures used for shaping and orienting alight beam. An individual component of this type is termed an optic.

In the context of the present disclosure, the term “scattered light” isused generally to include light that is reflected and backscattered froman object.

In the context of the present disclosure, the terms “viewer”,“operator”, and “user” are considered to be equivalent and refer to theviewing practitioner, technician, or other person who may operate acamera or scanner and may also view and manipulate an image, such as adental image, on a display monitor. An “operator instruction” or “viewerinstruction” is obtained from explicit commands entered by the viewer,such as by clicking a button on the camera or scanner or by using acomputer mouse or by touch screen or keyboard entry.

In the context of the present disclosure, the phrase “in signalcommunication” indicates that two or more devices and/or components arecapable of communicating with each other via signals that travel oversome type of signal path. Signal communication may be wired or wireless.The signals may be communication, power, data, or energy signals. Thesignal paths may include physical, electrical, magnetic,electromagnetic, optical, wired, and/or wireless connections between thefirst device and/or component and second device and/or component. Thesignal paths may also include additional devices and/or componentsbetween the first device and/or component and second device and/orcomponent.

In the context of the present disclosure, the term “camera” relates to adevice that is enabled to acquire a reflectance, 2-D digital image fromreflected visible or NIR light, such as structured light that isreflected from the surface of teeth and supporting structures.

The general term “scanner” relates to an optical system that projects ascanned light beam of broadband near-IR (BNIR) light that is directed tothe tooth surface through a sample arm and acquired, as scattered lightreturned in the sample arm, for detecting interference with light from areference arm used in OCT imaging of a surface. The term “rasterscanner” relates to the combination of hardware components that scanlight toward a sample, as described in more detail subsequently.

The term “subject” refers to the tooth or other portion of a patientthat is being imaged and, in optical terms, can be considered equivalentto the “object” of the corresponding imaging system.

In the context of the present disclosure, the phrase “broadband lightemitter” refers to a light source that emits a continuous spectrumoutput over a range of wavelengths at any given point of time.Short-coherence or low-coherence, broadband light sources can include,for example, super luminescent diodes, short-pulse lasers, many types ofwhite-light sources, and supercontinuum light sources. Most shortcoherence length sources of these types have a coherence length on theorder of tens of microns or less.

In the context of the present disclosure, the term “oblique” describesan angular orientation that is not an integer multiple of 90 degrees.Two lines or light paths can be considered to be oblique with respect toeach other, for example, if they diverge from or converge toward eachother at an angle that is about 5 degrees or more away from parallel, orabout 5 degrees or more away from orthogonal.

In the context of the present disclosure, two wavelengths can beconsidered to be “near” each other when within no more than +/−10 nmapart.

According to an embodiment of the present disclosure, there is provideda programmable light source that can provide variable wavelengthillumination. The programmable light source can be used as aswept-source for scanned SS-OCT and other applications that benefit froma controllably changeable spectral pattern.

Referring to FIG. 1, there is shown a programmable filter 10 that isused for generating a desired pattern and sequence of wavelengths (λ0 .. . λn) from a low-coherence, broadband light source. Broadband lightfrom a fiber laser or other source is directed, through a circulator 14through an optical fiber or other waveguide 12 to a collimator lens L1that directs the collimated light to a light dispersion optic 20, suchas a diffraction grating. Light dispersion optic 20 forms a spectrallydispersed output beam 24, directed toward a focusing lens L2. Lens L2focuses the dispersed light onto a spatial light modulator 80, such as amicro-mirror array 30. The micro-mirror array can be a linear array ofreflective devices or a linear portion of a Digital Light Processor(DLP) from Texas Instruments, Dallas, Tex. One or more individualreflectors in array 30 is actuated to reflect light of correspondingwavelengths back through the optical path. This reflected light is theoutput of programmable filter 10 and can be used in applications such asoptical coherence tomography (OCT) as described subsequently. Rapidactuation of each successive reflector in array 30 allows sampling ofnumerous small spectral portions of a spectrally dispersed output beam,such as that provided in FIG. 1. For example, where the spatial lightmodulator 80 is a micro-mirror array 30 that has 2048 micro-mirrorelements in a single row, where the spectral range from one side of thearray 30 to the other is 35 nm, each individual micro-mirror can reflecta wavelength band that is approximately 0.017 nm wide. One typical sweptsource sequence advances from lower to higher wavelengths by actuating asingle spatial light modulator 80 pixel (reflective element) at a time,along the line formed by the spectrally dispersed output beam. Otherswept source sequences are possible, as described subsequently.

The micro-mirror array 30 described herein and shown in FIGS. 1-3 andfollowing is one type of possible spatial light modulator 80 that can beused as part of a programmable light source. The spatial light modulator80 that is employed is a reflective device of some type, with discretelyaddressable elements that effectively provide the “pixels” of thedevice.

Programmable filter 10 resembles aspects of a spectrometer in itsoverall arrangement of components and in its light distribution.Incident broadband BNIR light is dispersed by light dispersion optic 20in order to spatially separate the spectral components of the light. Themicro-mirror array 30 or other type of spatial light modulator 80, asdescribed in more detail subsequently, is disposed to reflect a selectedwavelength band or bands of this light back through programmable filter10 so that the selected wavelength band can be used elsewhere in theoptical system, such as for use in an interferometry measurement deviceor for tuning a laser.

The simplified schematic of FIG. 2A and enlargement of FIG. 2B show howprogrammable filter 10 operates to provide light of a selectedwavelength band WI. FIG. 2B, which schematically shows a greatlyenlarged area E of micro-mirror array 30, shows the behavior of threemirrors 32 a, 32 b, and 32 c with respect to incident light of beam 24.Each mirror 32 element of micro-mirror array 30 can have either of twostates: deactuated, tilted at one angle, as shown at mirrors 32 a and 32b; or actuated, tilted at an alternate angle as shown at mirror 32 c.For DLP devices, the tilt angles for deactuated/actuated states of themicro-mirrors are +12 and −12 degrees from the substrate surface. Thus,in order to direct light back along optical axis OA through lens L2 andthrough the other components of programmable filter 10, micro-mirrorarray 30 is itself tilted at +12 degrees relative to the optical axisOA, as shown in FIG. 2B.

In the programmable filter 10 of FIG. 1, light dispersion optic 20 canbe a diffraction grating of some type, including a holographicdiffraction grating, for example. The grating dispersion equation is:

mλ=d(sin α+sin β)  (eq. 1)

wherein:

-   -   λ is the optical wavelength;    -   d is the grating pitch;    -   α is the incident angle (see FIGS. 1, 2A), relative to a normal        to the incident surface of optic 20;    -   β is the angle of diffracted light, relative to a normal to the        exit surface of optic 20;    -   m is the diffraction order, generally m=1 with relation to        embodiments of the present disclosure.

The FWHM (full-width half-maximum) bandwidth is determined by thespectral resolution of the grating δλ_(g) and wavelength range on apixel or micro-mirror 32 of the DLP device δλ_(DLP), which are given as:

δλ_(g) =λcd cos α/D  (eq. 2)

and

δλ_(DLP) =dp cos β/f.  (eq. 3)

wherein:

-   -   D is the 1/e² width of the incident Gaussian beam collimated by        lens L1;    -   λc is the central wavelength;    -   d is the grating pitch;    -   p is the DLP pixel pitch, for each micro-mirror;    -   f is the focus length of focus lens L2.

The final FWHM bandwidth δλ is the maximum of (δλ_(g), δλ_(DPL)).Bandwidth δλ defines the finest tunable wavelength range. For a suitableconfiguration for OCT imaging, the following relationship holds:

δλ_(g)≤δλ_(DLP).

In order to use the DLP to reflect the light back to the waveguide 12fiber, the spectrally dispersed spectrum is focused on the DLP surface,aligned with the hinge axis of each micro-mirror 32. The DLP referenceflat surface also tilts 12 degrees so that when a particularmicro-mirror 32 is in an “on” state, the light is directly reflectedback to the optical waveguide 12. When the micro-mirror is in an “on”state, the corresponding focused portion of the spectrum, with bandwidthcorresponding to the spatial distribution of light incident on thatmicro-mirror, is reflected back to the waveguide 12 fiber along the samepath of incident light, but traveling in the opposite direction.Circulator 14 in the fiber path guides the light of the selectedspectrum to a third fiber as output. It can be readily appreciated thatother types of spatial light modulator 80 may not require orientation atan oblique angle relative to the incident light beam, as was shown inthe example of FIG. 2B.

The 1/e² Gaussian beam intensity diameter focused on a single DLP pixelis as follows:

w=4λf/(πD cos β/cos α)  (eq. 4)

Preferably, the following holds: w≤p. This sets the beam diameter w atless than the pixel pitch p. The maximum tuning range is determined by:

M×δλ _(DLP),

wherein M is the number of DLP micro-mirrors in the horizontaldirection, as represented in FIG. 3. As FIG. 3 shows, the array ofmicro-mirrors for micro-mirror array 30 has M columns and N rows. Only asingle row of the DLP micro-mirror array is needed for use withprogrammable filter 10; the other rows above and below this single rowmay or may not be used.

The wavelength in terms of DLP pixels (micro-mirrors) can be describedby the following grating equation:

$\begin{matrix}{\lambda_{i} = {d( {{\sin \; \alpha} + {\sin ( {{\tan^{- 1}\lbrack {\frac{p}{f}( {\frac{N}{2} - i - 1} )} \rbrack} + \beta} )}} )}} & ( {{eq}.\mspace{14mu} 5} )\end{matrix}$

Wherein i is an index for the DLP column, corresponding to theparticular wavelength, in the range between 0 and (M−1).

From the above equation (5), the center wavelength corresponding to eachmirror in the row can be determined.

FIG. 4 shows programmable filter 10 in an alternate embodiment, with aprism 16 as light dispersion optic 20. The prism 16 disperses the lightwavelengths (λn . . . λ0) in the opposite order from the grating shownin FIG. 1. Longer wavelengths (red) are dispersed at a higher angle,shorter wavelengths (blue) at lower angles.

Conventional light dispersion optics distribute the dispersed light sothat its constituent wavelengths have a linear distribution. That is,the wavelengths are evenly spaced apart along the line of dispersedlight. However, for Fourier domain OCT processing, conversion ofwavelength data to frequency data is needed. Wavelength data (λ in unitsof nm) must thus be converted to wave-number data (k=λ⁻¹), proportionalto frequency. In conventional practice, an interpolation step is used toachieve this transformation, prior to Fourier transform calculations.The interpolation step requires processing resources and time. However,it would be most advantageous to be able to select wave-number k valuesdirectly from the programmable filter. The schematic diagram of FIG. 5shows one method for optical conversion of wavelength (λ₀ . . . λ_(N))data to wave-number (k₀ . . . k_(N)) data using an intermediate prism34. Methods for specifying prism angles and materials parameters forwavelength-to-wavenumber conversion are given, for example, in anarticle by Hu and Rollins entitled “Fourier domain optical coherencetomography with a linear-in-wavenumber spectrometer” in OPTICS LETTERS,Dec. 15, 2007, vol. 32 no. 24, pp. 3525-3527.

Programmable filter 10 is capable of providing selected lightwavelengths from a broadband light source in a sequence that isappropriately timed for functions such as OCT imaging using a tunedlaser. Because it offers a programmable sequence, the programmablefilter 10 can perform a forward spectral sweep from lower to higherwavelengths as well as a backward sweep in the opposite direction, fromhigher to lower wavelengths. A triangular sweep pattern, generation of a“comb” of wavelengths, or arbitrary wavelength pattern can also beprovided.

For OCT imaging in particular, various programmable sweep paradigms canbe useful to extract moving objects in imaging, to improve sensitivityfall-off over depth, etc. The OCT signal sensitivity decreases withincreasing depth into the sample, with depth considered to extend in thez-axis direction. Employing a comb of discrete wavelengths, for example,can increase OCT sensitivity. This is described in an article byBajraszewski et al. entitled “Improved spectral optical coherencetomography using optical frequency comb” in Optics Express, Vol. 16 No.6, March 2008, pp. 4163-4176.

The simplified schematic diagrams of FIGS. 6A and 6B each show aswept-source OCT (SS-OCT) apparatus 100 using programmable filter 10according to an embodiment of the present disclosure. In each case,programmable filter 10 is used as part of a tuned laser 50. Forintraoral OCT, for example, laser 50 can be tunable over a range offrequencies (wave-numbers k) corresponding to wavelengths between about400 and 1600 nm. According to an embodiment of the present disclosure, atunable range of 35 nm bandwidth centered about 830 nm is used forintraoral OCT.

In the FIG. 6A embodiment, a Mach-Zehnder interferometer system for OCTscanning is shown. FIG. 6B shows components for a Michelsoninterferometer system. For these embodiments, programmable filter 10provides part of the laser cavity to generate tuned laser 50 output. Thevariable laser 50 output goes through a coupler 38 and to a sample arm40 and a reference arm 42. In FIG. 6A, the sample arm 40 signal goesthrough a circulator 44 and to a probe 46 for measurement of a sample S.The sampled signal is directed back through circulator 44 (FIG. 6A) andto a detector 60 through a coupler 58. In FIG. 6B, the signal goesdirectly to sample arm 40 and reference arm 42; the sampled signal isdirected back through coupler 38 and to detector 60. The detector 60 mayuse a pair of balanced photodetectors configured to cancel common modenoise. A control logic processor (control processing unit CPU) 70 is insignal communication with tuned laser 50 and its programmable filter 10and with detector 60 and obtains and processes the output from detector60. CPU 70 is also in signal communication with a display 72 for commandentry and OCT results display.

The schematic diagram of FIG. 7 shows components of tuned laser 50according to an alternate embodiment of the present disclosure. Tunedlaser 50 is configured as a fiber ring laser having a broadband gainmedium such as a semiconductor optical amplifier (SOA) 52. Two opticalisolators OI provide protection of the SOA from back-reflected light. Afiber delay line (FDL) determines the effective sweep rate of the laser.Filter 10 has an input fiber and output fiber, used to connect the fiberring.

The schematic diagram of FIG. 8 shows the use of programmable filter 10for selecting a wavelength band from a broadband light source 54, suchas a super luminescent diode (SLD). Here, spatial light modulator 80reflects a component of the broadband light through circulator 14.Circulator 14 is used to direct light to and from the programmablefilter 10 along separate optical paths.

As shown in the schematic diagram of FIG. 9, galvo mirrors 94 and 96cooperate to provide the raster scanning needed for OCT imaging. In thearrangement that is shown, galvo mirror 1 (94) scans the wavelengths oflight to each point 82 along the sample to generate data along a row,which provides the B-scan, described in more detail subsequently. Galvomirror 2 (96) progressively moves the row position to provide 2-D rasterscanning to additional rows. At each point 82, the full spectrum oflight provided using programmable filter 10, pixel by pixel of thespatial light modulator 80 (FIGS. 1, 4, 5), is rapidly generated in asingle sweep and the resulting signal measured at detector 60 (FIGS. 6A,6B).

Scanning Sequence for OCT Imaging

The schematic diagrams of FIGS. 10A and 10B show a scan sequence thatcan be used for forming tomographic images using the OCT apparatus ofthe present disclosure. The sequence shown in FIG. 10A shows how asingle B-scan image is generated. A raster scanner 90 (FIG. 9) scans theselected light sequence over sample S, point by point. A periodic drivesignal 92 as shown in FIG. 10A is used to drive the raster scanner 90galvo mirrors to control a lateral scan or B-scan that extends acrosseach row of the sample, shown as discrete points 82 extending in thehorizontal direction in FIGS. 10A and 10B. At each of a plurality ofpoints 82 along a line or row of the B-scan, an A-scan or depth scan,acquiring data in the z-axis direction, is generated using successiveportions of the selected wavelength band. FIG. 10A shows drive signal 92for generating a straightforward ascending sequence using raster scanner90, with corresponding micro-mirror actuations, or other spatial lightmodulator pixel-by-pixel actuation, through the wavelength band. Theretro-scan signal 93, part of drive signal 92, simply restores the scanmirror back to its starting position for the next line; no data isobtained during retro-scan signal 93.

It should be noted that the B-scan drive signal 92 drives the galvomirror 94 for raster scanner 90 as shown in FIG. 9. At each incrementalposition, point 82 along the row of the B-scan, an A-scan is obtained.To acquire the A-scan data, tuned laser 50 or other programmable lightsource sweeps through the spectral sequence that is controlled byprogrammable filter 10 (FIGS. 1, 2A, 4, 5). Thus, in an embodiment inwhich programmable filter 10 causes the light source to sweep through a30 nm range of wavelengths, this sequence is carried out at each point82 along the B-scan path. As FIG. 10A shows, the set of A-scanacquisitions executes at each point 82, that is, at each position of thescanning galvo mirror 94. By way of example, where a DLP micro-mirrordevice is used as spatial light modulator 80, there can be 2048measurements for generating the A-scan at each position 82.

FIG. 10A schematically shows the information acquired during eachA-scan. An interference signal 88, shown with DC signal content removed,is acquired over the time interval for each point 82, wherein the signalis a function of the time interval required for the sweep, with thesignal that is acquired indicative of the spectral interference fringesgenerated by combining the light from reference and feedback arms of theinterferometer (FIGS. 6A, 6B). The Fourier transform generates atransform T for each A-scan. One transform signal corresponding to anA-scan is shown by way of example in FIG. 10A.

From the above description, it can be appreciated that a significantamount of data is acquired over a single B-scan sequence. In order toprocess this data efficiently, a Fast-Fourier Transform (FFT) is used,transforming the time-based signal data to corresponding frequency-baseddata from which image content can more readily be generated.

In Fourier domain OCT, the A scan corresponds to one line of spectrumacquisition which generates a line of depth (z-axis) resolved OCTsignal. The B scan data generates a 2-D OCT image along thecorresponding scanned line.

Raster scanning is used to obtain multiple B-scan data by incrementingthe raster scanner 90 acquisition in the C-scan direction. This isrepresented schematically in FIG. 10B, which shows how 3-D volumeinformation is generated using the A-, B-, and C-scan data.

As noted previously, the wavelength or frequency sweep sequence that isused at each A-scan point 82 can be modified from the ascending ordescending wavelength sequence that is typically used. Arbitrarywavelength sequencing can alternately be used. In the case of arbitrarywavelength selection, which may be useful for some particularimplementations of OCT, only a portion of the available wavelengths areprovided as a result of each sweep. In arbitrary wavelength sequencing,each wavelength can be randomly selected, in arbitrary sequential order,to be used in the OCT system during a single sweep.

The schematic diagram of FIG. 11 shows probe 46 and support componentsfor forming an intraoral OCT imaging system 62. An imaging engine 56includes the light source, fiber coupler, reference arm, and OCTdetector components described with reference to FIGS. 6A-7. Probe 46, inone embodiment, includes the raster scanner 90 or sample arm, but mayoptionally also contain other elements not provided by imaging engine56. CPU 70 includes control logic and display 72.

The preceding description gives detailed description of OCT imagingsystem 62 using a DLP micro-mirror array 30 as one useful type ofspatial light modulator that can be used for selecting a wavelength bandfrom programmable filter 10. However, it should be noted that othertypes of spatial light modulator 80 could be used to reflect light of aselected wavelength band. A reflective liquid crystal device couldalternately be used in place of DLP micro-mirror array 30, for example.Other types of MEMS (micro-electromechanical system devices)micro-mirror array that are not DLP devices could alternately be used.

Processing for OCT Imaging

The logic flow diagram of FIG. 12 shows a sequence for OCT processing toobtain OCT imaging content along with a surface point cloud extractedfrom the OCT content according to an embodiment of the presentdisclosure. The raw 2-D spectral data 150 with numerous A scans per eachB scan is provided over a linear wavelength λ, provided as M lines withN pixels per line. A mapping 152 then provides a wave-number value k foreach corresponding wavelength Δ. A background subtraction 154 executes,calculated along the B direction for each k value, and a line ofbackground signal is obtained. Background subtraction 154, performed oneach A line, helps to remove fixed pattern noise. In a zero paddingoperation 156 and a phase correction process 160 spectrum sampling iscorrected and dispersion-induced OCT signal broadening obtained. An FFTprocessing step 162 provides processing and scaling of thephase-corrected data to provide input for a 3-D volume rendering and 2-Dframe display rendering 166, useful for visualization and diagnosticsupport. At the conclusion of step 162, the OCT image content isavailable.

Subsequent processing in the FIG. 12 sequence then extracts the pointcloud for surface characterization. A segmentation step 170 is thenexecuted to extract the surface contour data from the OCT volume data.Object surface point cloud generation step 172 provides the surfacepoint clouds of the measured object. Point clouds can then be calibratedand used for mesh rendering step 174 along with further processing.Geometric distortion calibration of OCT images can be executed in orderto help correct shape distortion. Unless properly corrected, distortioncan result from the scanning pattern or from the optical arrangementthat is used. Distortion processing can use spatial calibration dataobtained by using a calibration target of a given geometry. Scanning ofthe target and obtaining the scanned data establishes a basis foradjusting the registration of scanned data to 3-D space, compensatingfor errors in scanning accuracy. The calibration target can be a 2-Dtarget, imaged at one or more positions, or a 3-D target.

Segmentation step 170, object surface point cloud generation step 172,and mesh generation and rendering step 174 of the FIG. 12 sequenceobtain surface contour data from OCT volume measurements. Importantly,results of these steps are the reconstructed surfaces of the objectmeasured by OCT. This extracted OCT surface imaging content can bedirectly merged with results measured by a surface contour imagingdevice that shares the same coordinate system as the OCT content, usingcoordinate matching methods commonly known in the art, such as iterativeclosest point (ICP) merging. OCT and surface contour image data contentcan thus be automatically registered, either as point clouds or mesh, byICP merging, without requiring additional steps.

The extracted OCT surface data, by itself or in registration withsurface contour image data, can be displayed, stored, or transmitted toanother computer or storage device.

Depending on applications and imaging conditions, various imagesegmentation algorithms can be used in segmentation step 170 to extractobject surfaces. Image segmentation algorithms such as simple directthreshold, active contour level set, watershed, supervised andunsupervised image segmentation, neural network based imagesegmentation, spectral embedding and max-flow/min-cut graph based imagesegmentation, etc. are well known in the image processing fields and canbe utilized; they can be applied to the entire 3-D volume or separatelyto each 2-D frame of the OCT data.

FIGS. 13A-13E show different types of imaging content acquired andgenerated as part of the OCT processing sequence, using the example of atooth image having a severe cavity. FIG. 13A shows a 2-D slice thatcorresponds to a B-scan for OCT imaging. FIG. 13B shows a depth-encodedcolor projection of the tooth, with an optional color bar 180 as areference. FIG. 13C shows a corresponding slice of the volume renderingobtained from the OCT imaging content. FIG. 13D shows the results ofsegmentation processing of FIG. 13A in which points along the toothsurface are extracted. FIG. 13E shows a surface point cloud 64 of thetooth generated from the OCT volume data. The surface point cloud 64 canbe obtained from the OCT volume data following segmentation, as shownpreviously with respect to the sequence of FIG. 12.

Surface Contour Imaging

Unlike OCT imaging described previously, surface contour imaging usesreflectance imaging and provides data for characterizing a surface, suchas surface structure, curvature, and contour characteristics, but doesnot provide information on material that lies below the surface. Contourimaging data or surface contour image data can be obtained from astructured light imaging apparatus or from an imaging apparatus thatobtains structure information related to a surface from a sequence of2-D reflectance images obtained using visible light illumination,generally in the range above about 380 and less than a 740 nm threshold,near-infrared light near and extending higher than 740 nm, orultraviolet light wavelengths below 380 nm. Alternate techniques forcontour imaging include structured light imaging as well as other knowntechniques for characterizing surface structure using reflectanceimaging techniques, such as feature tracking by triangulation,structure-from-motion photogrammetry, time-of-flight imaging, anddepth-from-focus imaging, for example. Contour image content canalternately be extracted from volume image content, such as from the OCTvolume content, as described previously with respect to FIG. 12, byidentifying and collecting only those voxels that represent surfacetissue, for example.

The phrase “patterned light” is used to indicate light that has apredetermined spatial pattern, such that the light has one or morefeatures such as one or more discernable parallel lines, curves, a gridor checkerboard pattern, or other features having areas of lightseparated by areas without illumination. In the context of the presentdisclosure, the phrases “patterned light” and “structured light” areconsidered to be equivalent, both used to identify the light that isprojected onto the subject in order to derive contour image data.

In structured light imaging, a pattern of lines, or other structuredpattern, is projected from the imaging apparatus toward the surface ofan object from a given angle. The projected pattern from the surface isthen viewed from another angle as a contour image, taking advantage oftriangulation in order to analyze surface information based on theappearance of contour lines. Phase shifting, in which the projectedpattern is incrementally shifted spatially for obtaining additionalmeasurements at the new locations, is typically applied as part ofstructured light imaging, used in order to complete the contour mappingof the surface and to increase overall resolution in the contour image.

FIG. 14 shows surface imaging using a pattern with multiple lines oflight. Incremental shifting of the line pattern and other techniqueshelp to compensate for inaccuracies and confusion that can result fromabrupt transitions along the surface, whereby it can be difficult topositively identify the segments that correspond to each projected line.In FIG. 14, for example, it can be difficult over portions of thesurface to determine whether line segment 116 is from the same line ofillumination as line segment 118 or adjacent line segment 119.

By knowing the instantaneous position of the scanner and theinstantaneous position of the line of light within an object-relativecoordinate system when the image was acquired, a computer equipped withappropriate software can use triangulation methods to compute thecoordinates of numerous illuminated surface points. As a result of thisimage acquisition, a point cloud of vertex points or vertices can beidentified and used to characterize the surface contour. The points orvertices in the point cloud then represent actual, measured points onthe three dimensional surface of an object.

The pattern can be imparted to the patterned light using a spatial lightmodulator, such as a Digital Light Processor (DLP) or using adiffraction grating, for example. The pattern can also be generated as araster pattern by actuated deflection of light emission coordinated withthe scanner hardware, such as by the use of a microelectrical-mechanicalsystem (MEMS) or a galvo.

It should be noted that reflectance imaging can be used for purposesother than surface contour imaging. Reflectance images of the toothsurface, for example, can be used for determining color, surfacetexture, and other visible characteristics of the tooth surface.

Combining OCT with Surface Contour and Other Reflectance Imaging

Certain exemplary method and/or apparatus embodiments can providecombined OCT and structured light imaging for dental imaging. Anembodiment of the present disclosure, shown in the simplified schematicdiagram of FIG. 15 as an imaging apparatus 200, provides an exemplarymechanism and methods that combine OCT and structured light imaging in asingle imaging apparatus for generating both depth-resolved tomographyimage content and a surface contour image content that can be readilyregistered to each other and acquired either simultaneously or nearlysimultaneously, that is, acquired in a single imaging operation ratherthan requiring separate scanning passes by the operator. Significantly,the imaging paths for OCT and surface contour imaging are spectrallyseparated, so that the wavelengths used in each imaging path aredistinct from each other. The light for OCT illumination imaging liesabove a threshold wavelength and the light for surface contour imagingbelow the threshold wavelength.

The simplified schematic diagram of FIG. 15 shows two imagingsubsystems, a reflectance imaging or surface contour imaging system 210and an OCT imaging system 220, that cooperate as part of imagingapparatus 200. Surface contour imaging system 210 uses visible light Visillumination that is conveyed to a sample S, such as a tooth. Accordingto an embodiment of the present disclosure, the Vis light wavelengthrange that is used extends from about 380 nm to about 740 nm and isdetected by a camera 212.

The OCT imaging system 220 in FIG. 15 uses BNIR light from a broadbandcoherent near-infrared light source used for OCT imaging with wavelengthranging from 740 nm to 1550 nm. A fiber coupler FC splits the BNIR lightinto reference arm 42 and sample arm 40. Light in reference arm 42 isretro-reflected by a reference mirror 222 and coupled to fiber couplerFC as reference light for interferometry, as described previously withreference to schematic diagrams of FIGS. 6A and 6B. Light in sample arm40 is conveyed to sample S such as a tooth via raster scanner 90 asshown schematically in FIG. 9 and supporting focusing opticalcomponents, not shown. A portion of the BNIR light that is backscatteredby the sample S is collected by the same optics of sample arm 40 andcoupled back to sample arm 40. The reference light and sample lightinterfere at fiber coupler FC.

The light paths for surface contour imaging system 210 and OCT imagingsystem 220 in FIG. 15 enter fiber coupler FC on the same path but arespectrally isolated from each other, above and below the thresholdvalue, as noted previously. Optionally, to provide additional isolationof the two systems, spectral filters can be employed. Spectral filter216, placed in between fiber coupler FC and OCT signal detector 224,ensures that only the broad band NIR interference light is detected byOCT signal detector 224. Camera 212 senses only visible light, and BNIRlight is blocked by a different spectral filter 214. The reflectedvisible light pattern is captured by camera 212 at an appropriate anglewith respect to the patterned Vis illumination direction. For surfacecontour imaging, a predetermined illumination pattern impinges ontosample S with modulation of visible light intensity, under control ofraster scanner 90.

Conveniently, the same raster scanner 90 and associated optics conveyboth the BNIR light for OCT and Vis patterned illumination for surfacecontour imaging to sample S. Because OCT and surface contour imagingshare the same raster scanner 90, when system calibration is done onimaging apparatus 200, both OCT and surface contour imaging areautomatically calibrated to the same coordinate system. A processor 230,in signal communication with both OCT signal detector 224 and relatedcomponents and with camera 212, controls and coordinates the behavior ofboth surface contour imaging system 210 and OCT imaging system 220 foracquisition of both OCT and surface contour image content.

The schematic diagram of FIG. 16A shows an embodiment of imagingapparatus 200 that combines raster scanner 90 and camera 212 optics asparts of a handheld probe 240 for intraoral imaging, wherein sample S isan intraoral feature such as a tooth, gum tissue or other supportingstructure. Components of probe 240 can alternately include additionalportions of the OCT imaging and reflective imaging components. Probe 240connects to processor 230 by means of wired connection, such as forsignal connection and electrical power, and provides optical signalsover an optical fiber cable connection.

Imaging apparatus 200 can work in either OCT depth imaging or surfacecontour imaging mode, operating in either mode separately, or capturingimage content in both modes simultaneously. In addition, the visiblelight source Vis and camera 212 can be used for preview only in supportof OCT imaging. FIG. 16A also shows a mode switch 226 that can be usedfor selection of operating mode, such as one of reflectance imaging, OCTimaging, or both imaging types. Alternately, mode switch 226 can resideon handheld probe 240 or can be a “soft” switch, toggled by operatorinstruction entry on the user interface of processor 230.

In one exemplary embodiment, OCT depth imaging can be retrofit to asurface contour imaging apparatus.

FIG. 16B is a schematic diagram showing an imaging apparatus thatcombines surface contour and OCT imaging and shows a visible lightsource providing the visible light Vis through coupler 38 and circulator44 for surface contour imaging. The visible light can share the sameoptical path used for providing sample light in the OCT imagingsub-system in probe 240. This allows simultaneous or near-simultaneousOCT and reflectance image capture, with the light from the OCT andvisible light Vis traveling along the same path. It should be noted thatthe OCT scan typically obtains only a few complete frames per second,whereas the reflectance imaging used for surface contourcharacterization or for color characterization of a tooth or othersurface can capture and process images at a much faster rate.

FIG. 16B shows the OCT imaging system with a Mach-Zehnder interferometerconfiguration and a swept-source OCT implementation only by way ofillustration. Alternative type of interferometer configurations, such asMichelson interferometer, can also be used. An alternative type of OCTimplementation, such as spectral-domain OCT or time-domain OCT, can alsobe used.

There are a number of arrangements that can be used for probe 240components. FIG. 17A shows a configuration using a single two-axisscanning mirror 250 as raster scanner 90. Single two-axis scanningmirror 250 can be a 2-axis MEMS mirror, for example. Optical componentsin an optical module 260 provide collimated light to scanning mirror250. Light from scanning mirror 250 is directed through an objectivelens L3 that focuses the collimated beam. An optional folding mirror 262folds the light path to direct the focal region to sample S and todirect reflected light to camera 212, which includes an imaging lens anda sensor (not shown separately). Light for both OCT and surface contour(reflectance) imaging is emitted from optical module 260. Thissimplifies calibration that registers the OCT imaging to the contoursurface imaging, or other reflectance imaging such as imaging forcharacterizing tooth color. Because the scanning mirror 250 position iscontrolled by processing logic, this position is known at each instant,whether the emitted light is BNIR light used for OCT imaging or Vislight used for reflectance imaging. Calibration of the scanning hardwareserves both OCT and reflectance imaging paths.

As shown schematically in FIG. 17A, an optional filter 214 can be usedwith camera 212 to further distinguish the OCT from the surface contourimaging path, rejecting OCT wavelengths and other unwanted light. Afilter 216 can be provided as part of optical module 260, for blockingVis light from reaching the OCT detector.

The schematic view of FIG. 17B shows a configuration that also usestwo-axis scanning mirror 250 as raster scanner 90. Optical components inoptical module 260 provide collimated light for both OCT and visiblelight systems to scanning mirror 250. Light from scanning mirror 250 isdirected through objective lens L3 that focuses the collimated beam.Folding mirror 262 folds the light path to direct the light to sample Sand form the focal region at camera 212. Lens L3 also forms part of theimaging path in the FIG. 17B arrangement, directing light to camera 212.

FIG. 17C is a schematic view that shows a probe 240 configuration usinga two-mirror 252, 253, two-axis raster scanner 90. Each mirror 252, 253is a single-axis mirror; it can be a galvo mirror or a single-axis MEMSmirror, for example. Optical module 260 directs collimated light tomirror 252, which scans about a first axis. The reflected light isdirected to mirror 253 that scans about a second axis and directs thelight through objective lens L3. Folding mirror 262 folds the light pathto direct the focal region to sample S and to direct reflected Vis lightto camera 212. Lens L3 also forms part of the imaging path in the FIG.17C arrangement, directing light to camera 212.

FIG. 17D is a schematic view wherein optical module 260 generatesfocused light, so that an external lens is not needed. Two-axis scanningmirror 250 directs this light to the sample S and directs image-bearinglight to camera 212.

FIGS. 17E and 17F are schematic diagrams showing alternate scanningarrangements in which another optical module 266 is used to provide Vislight. In this scanning arrangement, visible light Vis takes a separatepath to the handheld probe, unlike the arrangement shown in the diagramof FIG. 16B. Beamsplitter 264 combines Vis light from optical module 266and BNIR light from optical module 260 so that the two lights follow thesame path from beamsplitter 264 to sample S. In FIG. 17E, the generatedline is scanned toward sample S by single-axis mirrors 252, 253. FIG.17F shows an alternate embodiment using a single two-axis mirror 250 toshift line position for surface contour imaging.

As another option for surface contour characterization, surfacesegmentation can also be used to extract a point cloud representative ofa real surface from OCT images of an object. The extracted geometricshape of the point cloud matches that obtained with structured lightimaging method.

As noted previously, both the OCT and reflectance image content can beacquired with reference to the same raster scanner coordinates. Pointclouds generated from both systems also share the same coordinates. Oncesurface data is extracted from the OCT volume image by segmentation,registration of the surface data from OCT to the contour surface imagingoutput is simplified.

Light Source Options

Visible light Vis can be of multiple wavelengths in the visible lightrange. The Vis source can be used for color-coding of the projectedstructured light pattern, for example. The Vis source can alternately beused for white light image preview or for tooth shade measurement orcolor or texture characterization.

Vis light can be provided from a conventional bulb source or mayoriginate in a solid-state emissive device, such as a laser or one ormore light-emitting diodes (LEDs). Individual Red, Green, and Blue LEDsare used to provide the primary color wavelengths for reflectanceimaging.

In addition to providing a structured light pattern, the Vis source canalternately provide light of particular wavelengths or broadband lightthat is scanned over the subject for conventional reflectance imaging,such as for detecting tooth shade, for example, or for obtaining surfacecontour data by a method that does not employ a light pattern, such asstructure-from-motion imaging, for example.

A violet light, in the near-UV region can be used as the excitationlight for tooth fluorescence imaging. Backscattered fluorescence can becollected by the OCT light path. The fluorescence image can be detectedby the same detector path of the Fourier domain OCT, but at a differentlateral spectrum location.

FIG. 18 shows exemplary spectral values for light sources. In general,violet V wavelengths in the near UV region, below about 380 nm, aretypically favored for fluorescence imaging. The visible light Vis, withcomponents labeled B, G, R for primary Blue, Green, and Red colorsranging from above 380 to below 740 nm, is usually selected forstructured light pattern projection. Infrared light above 740 nm isusually selected for OCT imaging.

An embodiment of the present disclosure provides an active triangulationsystem for contour imaging that includes an illumination path that isshared by both an OCT system and a reflectance imaging system. Camera212 in the imaging path (FIGS. 17A-17F) views the sample at an obliqueangle with respect to the illumination path. The visible light sourceused for generating the structured light pattern emits light atdifferent wavelengths not used for the OCT system, so that the twooptical systems can operate without perceptible crosstalk orinterference between them. The visible light can encode a predeterminedlight pattern for structured light imaging by appropriately controllingthe timing of the visible light source with respect to motion of rasterscanner 90. Distorted light patterns from the subject surface are imagedby the optical system in the imaging path and captured by the camera.Decoding the light pattern generates the surface contour of the imagedobject.

Reconstruction of the 3D mesh corresponding to a full arch is usuallydone by acquiring a series of slightly overlapping intraoral 3D views,and stitching them together. The process of identifying which portion ofthe mesh under construction the newly acquired view overlaps with isreferred to as “matching”. An intraoral 3D scanner can use this processto generate a 3D mesh of an entire arch of a patient. However, asmatching is a surfacing process, minor local accuracy issues that can becumulative can occur. For example, as matching is a surfacing process, aslight angular error can be created, which, due to the accumulationprocess (e.g., from a back left molar around the incisors to a backright molar), usually results in a significant error after the entirearch has been reconstructed. Typically, a 200-micron right-to-left molarerror can be observed.

Certain exemplary method and/or apparatus embodiments can provideintraoral 3D mesh of an arch of a patient having reduced angular error.By using a scanner that has surface imaging (e.g., surface contourimaging) and penetrating abilities, exemplary method and/or apparatusembodiments herein can provide intraoral 3D mesh of a dental arch usinga matching process including the depth data to reduce minor localaccuracy issues that can be cumulative (e.g., which reduces the angularerror). In one exemplary embodiment, OCT technology is used forpenetrating capabilities. In another exemplary embodiment, technologiessuch as ultrasound or optoacoustic can be used for depth penetratingcapabilities.

Some exemplary method and/or apparatus embodiments can provide intraoral3D mesh of an arch of a patient having reduced angular error. In anexemplary embodiment, hard tissue that is not normally visible in the IOscans can provide a strong registration with 3D CBCT data to guaranteereduction in the 3D mesh arch distortion (e.g., full arch).

One exemplary method and/or apparatus embodiment can include two factorsthat can be applied to small and large span restorationsapplications/work:

The most complicated case for a fully edentulous case when there are noteeth remaining and the gum tissue has to be 3D optically scanned (e.g.,3D optically scan). The gum tissue has fewer land mark features, andthus, it can be a bigger challenge to complete the matching process(e.g., register the individual 3D contour images).

In one exemplary method and/or apparatus embodiment, first, with thepenetrating scan, it is possible to see the bone structure below the gumtissue. This means that when an image is taken we have the soft tissueand the hard tissue (e.g., non deformable imaging content). By combiningboth elements (soft tissue and the hard tissue) means that it ispossible firstly to associate the hard tissue and then use thispositioning information to correctly position the soft tissue as well.This exemplary embodiment will ensure a more precise registration of thedata sets (e.g., 3D contour images).

In the case of large span restorations and for example, the implantworkflow it is preferable to perform a 3D X-ray (CBCT) scan to evaluatethe suitability of the bone structure to accept an implant. In thissituation, the CBCT scan can provide a reference model that has nodistortion linked to the scanning process. In another exemplary methodand/or apparatus embodiment, the CBCT X-ray scan (and volumereconstruction) can be used as a default structure, to which the JO scandata (e.g., depth information) is matched. If there are cross archdeviations, in this case, the matched CBCT scan reconstruction and theJO scanner depth information can be used to rectify (e.g., rigidly ornon rigidly the IO data set is matched to the 3D X-ray data set), the 3Dsurface mesh of the JO scan can have a reduced or minimum distortionacross the object or full dental arch.

FIG. 19 illustrates an embodiment of an extra-oral imaging apparatus 10.Apparatus 10 comprises a support structure that includes a support frame12 which may be a support column. The column 12 may be adjustable in twoor three dimensions. For example, the column 12 can be telescopic andmay include an upper part 12 a that is slidably mounted over a fixedlower part 12 b.

The support structure also includes a horizontal mount 14 that may besupported or held by the vertical column 12. Horizontal mount 14 extendsaway from vertical column 12 and may be substantially perpendicularthereto. Horizontal mount 14 can move relative to the vertical column12. More particularly, horizontal mount 14 is fixedly mounted on thevertical upper part 12 a and is therefore movable therewith. Forexample, an actuator, e.g. of the electric type, located behind thevertical column (not represented in the drawing) can be commanded todrive the horizontal mount 14 into a vertical movement in a controlledmanner. Horizontal mount 14 can support a gantry 16. Gantry 16 ismovable relative to the support structure, and more particularly tohorizontal mount 14. Gantry 16 may more particularly be rotatablerelative to horizontal mount 14. Gantry 16 may be rotatable about avertical axis of rotation, which may be still during the operation ofthe imaging process or may follow one among several predeterminedtrajectories, in accordance with the selected imaging process. A drivingknown mechanism (not represented) for driving the gantry 16 into a givenmovement is integrated inside horizontal mount 14. By way of example,such driving mechanism includes motors for imparting a first movement ina X, Y plane, e.g. two step by step motors, and a motor for imparting arotational movement about the vertical axis Z, e.g. a brushless motor.

Gantry 16 supports both an x-ray source 18 and at least one x-ray sensor20 that is arranged in correspondence with the x-ray source. X-raysource 18 and the at least one x-ray sensor 20 may be arranged facingeach other. Gantry 16 may include two opposite downwardly extendingarms: a first arm 16 a supports x-ray source 18 that is attached theretoand a second opposite arm 16 b supports the at least one x-ray sensor 20that is attached thereto.

When activated x-ray source 18 emits an x-ray beam which radiates all orpart of an imaging area, e.g., a working area for placement of thepatient's head, before impinging the at least one x-ray sensor 20.

In the present embodiment, the at least one x-ray sensor 20 may includea panoramic sensor, e.g. a slit-shaped sensor, a volumetric orcomputerized sensor (e.g. rectangular, square-shaped) or a cephalometricsensor or several sensors.

Depending on the sensor or sensors present in the apparatus, one orseveral operating modes or imaging processes (1, 2 or 3) may be usedamong the panoramic, volumetric or computerized tomography, andcephalometric modes.

The support structure may also include a patient positioning arm 22 thatis connected to the support frame, and more particularly to the verticalcolumn 12. The patient positioning arm 22 is movable relative to thesupport frame. More particularly, arm 22 can slide along the verticalcolumn 12 so as to move up or down upon command. The patient positioningarm 22 extends from an arm support 22 a that is slidably mountedrelative to the fixed lower part vertical column 12 b. The patientpositioning arm 22 extends along the apparatus in a direction that issubstantially in correspondence with the direction of extension ofhorizontal mount 14. Patient positioning arm 22 is arranged sidewaysrelative to the apparatus in a substantial parallel relationship withhorizontal mount 14. For example, an actuator, e.g. of the electrictype, located behind the vertical column (not represented in thedrawing) can be commanded to drive the arm support 22 a into a verticalmovement in a controlled manner.

Patient positioning arm 22 serves to position the patient in theapparatus at a given location. In one embodiment, the patientpositioning atm 22 can position the patient in the imaging areaaccording to selection of an operating modes of the apparatus 10.

Patient positioning arm 22 may include one or more patient positioningand/or holding systems generally located at a free end 22 b of the armor proximate thereto.

One or more patient positioning and/or holding systems allow to positionthe anatomical structures of the patient's head according to differentorientations and to immobilize the patient's head during the examinationso as to reduce any possible movement.

There exists one or several systems for each type of examination to becarried out. The arm 22 is configured to accommodate these systems.

As illustrated in FIG. 19, one of these systems, noted 24, includes twotemporal holding members that extend upwardly from the arm 22 to whichthey are removably attached. Only one temporal holding member isrepresented, the other one being hidden by the arm 16 b.

Another illustrated system is a chin support 26 that extends upwardlyfrom the arm 22 to which it is removably attached. The chin support 26can be located between the two temporal holding members.

Other possible attachable, movable or integrated systems may beenvisaged: a nasal support, a bite support etc.

A handle assembly 28 may be positioned at the free end 22 b of the arm,underneath the arm and in a parallel relationship with the arm. Thishandle assembly 28 includes two vertical separate handle portions 28 a,28 b which can be grasped by the patient when undergoing an imagingprocess so as to remain motionless.

Overall this handle assembly 28 has a U-shape which can include ahorizontal base portion 28 c and two vertical upwardly-extendingbranches 28 a, 28 b that are fixed to the arm 22. Each branch plays therole of a vertical handle portion.

Patient positioning arm 22 also supports a monitor or display assembly30 which makes it possible for a user of the apparatus to view and drivecertain functions of the apparatus.

The apparatus 10 further comprises a seat arrangement 40 that isconnected to the support frame 12. The seat arrangement 40 is movablebetween at least two distinct positions: —a working position in whichthe seat arrangement 40 is located in a working area with a prescribedspatial relationship to the gantry 16 and the horizontal mount 14 (FIG.19, e.g., below or under), —at least one rest position in which the seatarrangement 40 is located away from the working area so as to leaveclear the working area under the gantry 16.

Consistent with an embodiment of the present invention, a computerprogram utilizes stored instructions that perform on image data that isaccessed from an electronic memory. As can be appreciated by thoseskilled in the image processing arts, a computer program for operatingthe imaging system in an embodiment of the present disclosure can beutilized by a suitable, general-purpose computer system operating as CPU70 as described herein, such as a personal computer or workstation.However, many other types of computer systems can be used to execute thecomputer program of the present invention, including an arrangement ofnetworked processors, for example. The computer program for performingthe method of the present invention may be stored in a computer readablestorage medium. This medium may comprise, for example; magnetic storagemedia such as a magnetic disk such as a hard drive or removable deviceor magnetic tape; optical storage media such as an optical disc, opticaltape, or machine readable optical encoding; solid state electronicstorage devices such as random access memory (RAM), or read only memory(ROM); or any other physical device or medium employed to store acomputer program. The computer program for performing the method of thepresent disclosure may also be stored on computer readable storagemedium that is connected to the image processor by way of the internetor other network or communication medium. Those skilled in the art willfurther readily recognize that the equivalent of such a computer programproduct may also be constructed in hardware.

It should be noted that the term “memory”, equivalent to“computer-accessible memory” in the context of the present disclosure,can refer to any type of temporary or more enduring data storageworkspace used for storing and operating upon image data and accessibleto a computer system, including a database, for example. The memorycould be non-volatile, using, for example, a long-term storage mediumsuch as magnetic or optical storage. Alternately, the memory could be ofa more volatile nature, using an electronic circuit, such asrandom-access memory (RAM) that is used as a temporary buffer orworkspace by a microprocessor or other control logic processor device.Display data, for example, is typically stored in a temporary storagebuffer that is directly associated with a display device and isperiodically refreshed as needed in order to provide displayed data.This temporary storage buffer is also considered to be a type of memory,as the term is used in the present disclosure. Memory is also used asthe data workspace for executing and storing intermediate and finalresults of calculations and other processing. Computer-accessible memorycan be volatile, non-volatile, or a hybrid combination of volatile andnon-volatile types.

It will be understood that the computer program product of the presentdisclosure may make use of various image manipulation algorithms andprocesses that are well known. It will be further understood that thecomputer program product embodiment of the present disclosure may embodyalgorithms and processes not specifically shown or described herein thatare useful for implementation. Such algorithms and processes may includeconventional utilities that are within the ordinary skill of the imageprocessing arts. For example, matching algorithm for registering 3Dvolume sets are known to one of ordinary skill in the dental 3D imagingor restoration technology. Additional aspects of such algorithms andsystems, and hardware and/or software for producing and otherwiseprocessing the images or co-operating with the computer program productof the present disclosure, are not specifically shown or describedherein and may be selected from such algorithms, systems, hardware,components and elements known in the art.

Certain exemplary method and/or apparatus embodiments according to theapplication can provide reduced errors in generating a dental arch 3Dsurface mesh. Exemplary embodiments according to the application caninclude various features described herein (individually or incombination).

While the invention has been illustrated with respect to one or moreimplementations, alterations and/or modifications can be made to theillustrated examples without departing from the spirit and scope of theappended claims. In addition, while a particular feature of theinvention can have been disclosed with respect to only one of severalimplementations/embodiments, such feature can be combined with one ormore other features of the other implementations/embodiments as can bedesired and advantageous for any given or particular function. The term“at least one of” is used to mean one or more of the listed items can beselected. The term “about” indicates that the value listed can besomewhat altered, as long as the alteration does not result innonconformance of the process or structure to the illustratedembodiment. Finally, “exemplary” indicates the description is used as anexample, rather than implying that it is an ideal. Other embodiments ofthe invention will be apparent to those skilled in the art fromconsideration of the specification and practice of the inventiondisclosed herein. It is intended that the specification and examples beconsidered as exemplary only, with a true scope and spirit of theinvention being indicated by at least the following claims.

1. An optical apparatus for imaging a sample, the apparatus comprising:an optical coherence tomography imaging apparatus having: a) a firstlight source that generates low coherence light of wavelengths above athreshold wavelength; b) a signal detector that obtains an interferencesignal between a first portion of the low coherence light scattered fromthe sample and a second portion of the low coherence light reflectedfrom a reference; a surface contour imaging apparatus having: a) asecond light source that emits one or more wavelengths of surfaceillumination below the threshold wavelength; b) a camera disposed at anoblique angle with respect to the direction of the surface illuminationincident at the sample to acquire images from the illumination reflectedfrom the sample; a probe that has a raster scanner wherein the lowcoherence light and the surface illumination share the same path fromthe raster scanner to the sample; and a processor that is programmedwith instructions that coordinate activation of the first and secondlight sources, actuation of the raster scanner, and acquisition of datafrom the signal detector and the camera and further programmed withinstructions to display, store, or transfer images from the acquireddata.
 2. The apparatus of claim 1 wherein the sample is an intraoralfeature.
 3. The apparatus of claim 1, where the optical coherencetomography imaging apparatus and surface contour imaging apparatusacquire data simultaneously or near-simultaneously, and where theinterference signal is obtained from a Michelson or Mach-Zehnderinterferometer.
 4. A method for imaging a sample comprising: a)obtaining optical coherence tomography imaging content with steps of:(i) generating low coherence light of wavelengths above a thresholdwavelength; (ii) obtaining an interference signal between a firstportion of the low coherence light scattered from the sample and asecond portion of the low coherence light reflected from a reference; b)obtaining surface contour imaging content; c) simultaneously to step b)obtaining depth imaging content associated to the obtained surfacecontour imaging content; d) segmenting among the depth imaging content anon deformable imaging content; and where optical coherence tomographyimaging and surface contour imaging content are obtained and mapped tothe same coordinate system using the non deformable content.
 5. Themethod according to claim 4, where the non deformable content compriseshard tissues.
 6. The method according to claim 4, where the methodfurther comprises: providing a CBCT scan 3D image of the sample;registering the non deformable content with CBCT Scan 3D image
 7. Themethod according to claim 6 wherein the method further comprises thestep of resealing the CBCT Scan 3D image of the sample.